Aeroflot Flight 3352 was a Tupolev Tu-154airline flight on a domestic route from Krasnodar to Novosibirsk, with an intermediate landing in Omsk. While landing at Omsk Airport on Thursday, 11 October 1984, the aircraft crashed into maintenance vehicles on the runway, killing 174 people on board and 4 on the ground. While a chain of mistakes in airport operations contributed to the accident, its major cause was an air traffic controller falling asleep on duty. As of 2015, this remains the deadliest aviation accident on Russian territory.[1][2][3][4][5]

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At 5:00 am local time (UTC/GMT + 7 hours), Flight 3352 was preparing to land at Tsentralny Airport in Omsk, a key Russian city in southwestern Siberia, which has a population of over 1 million and is the administrative center of Omsk Oblast. At the time, this was the only aircraft approaching Omsk, and it was cleared for landing when it contacted the airport.[3][5]

At 5:20 am, worried that the continuing rain would make the runway overly slippery, the airport ground maintenance crew requested permission to dry the runway. The ground controller on duty gave permission and proceeded to fall asleep soon after, in the process forgetting to switch on the "runway occupied" warning. In any case, under airport regulations, this whole procedure should never have happened; permission to close and do maintenance on a runway could only be given by the chief controller, and he was absent.

The maintenance crew, following the airport's routine, moved three vehicles to the runway: a UAZ-469all-terrain vehicle with an attached trailer, operated by a driver and crew manager in front; followed by KrAZ and Ural trucks. The latter were equipped with dry air compressors and loaded with fuel, and weighed 16–20 tons. The drying detail then proceeded to violate their own safety rules while performing their tasks: all of their vehicles should have their top, flickering lights on continuously. However, the lights were too bright for the maintenance workers' liking, so they kept them lit only until they started and after they finished their work.

This intentional oversight was to play a part in the pilots being unable to see the vehicles on the runway (they could not from the air).[3][5] In contrast, the runway crew saw the Tu-154 coming at them from a good distance, its landing lights on. They did attempt to contact ground control three times about the lights, but received no response and so ignored them, thinking they were being tested by a plane not on final approach.[3][5]

UAZ-469

Around 5:36 am, Flight 3352 requested permission to land from the approach controller. The request was sent twice; the pilots noticed vague contours on the runway and wanted to double check for obstacles. The controller verified the runway status, which remained apparently unoccupied, then contacted the ground controller and received no response, and subsequently contacted the flight controller on internal radio and received an inaudible reply that sounded like "..ree" (original, Russian: ..бодна) and was taken as "free" (Russian: свободна; communications were being taped and were analyzed later). The approach controller cleared the landing, though unable to see the runway, and in spite of regulations that required him to keep the flight in the air and double check the runway's status. Both the ground controller and secondary controller should have been able to see the runway, but the former was asleep,[1] and the latter was absent due to staff shortages.

At 5:38 am, the flight passed the lowest height at which the flight crew could abort the landing. The aircraft landed at a normal 240 km/h (149 mph/130 knots). On touchdown, the flight crew saw the array of drying vehicles and attempted to turn the aircraft, but were unable to avoid the collision. The plane crashed into the Ural truck and then 200 m down the runway crashed into the KrAZ, igniting the 7 tons of fuel in each truck and the aircraft's fuel tank. The plane overturned and broke into pieces, some of which crashed into the UAZ-469. A catastrophic fracture of the fuel tanks caused burning fuel to leak into the fuselage, incinerating all but one passenger. The cockpit section detached and flew past the burning vehicles. It suffered no major damage, and all four crew members survived, suffering only minor injuries.[1][3][4][5] They escaped from the cabin and ran to the crash site in an attempt to help the passengers. Four ground maintenance crew were killed instantly inside the vehicles. One survivor in the passenger seat of the UAZ caught on fire, which was extinguished.[5]

A State investigation concluded that the accident was caused by a chain of mistakes owing to the negligence of air traffic controllers, as well as disobedience of basic airport maintenance and safety regulations. The ground controller was found directly responsible, as he fell asleep on the job and thus did not respond to emergency queries; he also allowed the service trucks to move onto the runway and did not mark the runway as occupied. At a hearing, he could not recollect his actions during the time in question, but did not deny the charges. He was sentenced to 15 years and committed suicide in prison.[3][5] In addition, the flight operations manager was sentenced to 15 years in prison, the approach controller to 13 years, and the head of airport maintenance to 12 years.[3] All three appealed their sentences, to no avail. Future inspections at numerous other Soviet airports also found similar types and numbers of violations of safety regulations, resulting in the firing of several high-level officials thereafter.[5]

No pilot error or aircraft deficiency was found. Flight mass and centering were within norms. Owing to poor visibility, the crew could not detect the obstructions on the runway. While they did have some reasonable doubts as to whether or not the runway was occupied, these were allayed by the approach controller's reassurances. The crew had only a few seconds to avoid the collision on the ground; they took evasive action, but could not possibly save the aircraft.[6] They were thus absolved of any blame.

The flight controller and approach controller were experienced professionals with at least 10 years of service. The ground controller on duty, who was 23 years old, was new. He supposedly had not had enough sleep in the days before the accident, having had to care for his two young children.

The formal hearing of the case occurred only 3 months after the accident, due to the obvious set of circumstances; most of that time was spent on identifying the victims and locating their relatives. All of the accused, as well as their attorneys, received threats and were moved to the hearings under heavy security.[5]

At the time it took place, the accident was the deadliest one in Soviet aviation history. It was surpassed on 10 July 1985 by Aeroflot Flight 7425, another Tu-154, which crashed in Uzbek SSR (modern day Uzbekistan), and killed 200 people.[1][2]